Quick heat electric heating unit



Oct 2, 1956 J. L sHRoYER QUICK HEAT ELECTRIC HEATING UNIT Filed Nov. 18,1953 MMV nited States Patent O i QUICK HEAT ELECTRIC HEATING UNIT JacobL. Shroyer, Oak Park, Ill., assignor to Tuttle & Kift, Inc., Chicago,Ill., a corporation of Illinois Application November 18, 1953, SerialNo. 392,798

3 Claims. (Cl. 219-37) My invention relates to electric heating units ofthe metal sheathed type such as commonly employed in electric ranges forsurface heating, and has reference more particularly to facilities foroperating the unit temporarily at awattage suliiciently in excess ofnormal to heat up rapidly in starting.

Such units are made with one or more heating resistances embedded ininsulation in a metal sheath, and because of the mass of insulatingmaterial and sheath which must be heated, considerable delay isexperienced in bringing the unit to the desired operating temperatureunless the heating unit is adapted to temporarily supply heatinstarting, considerably in excess of that required in normal operation.

Water heaters have been made in which the entire heating resistance wasmade of a material having a high positive temperature coefiicient ofresistance to protect the heater against damage if not submerged andthese provide extra wattage during heating up periods, but suchresistance was not acceptable for open heaters, such, for example, asemployed in electric ranges, and accordingly it has been customary withsuch heaters to use standard resistances and merely provide controlstherefor which are operable to provide temporary connections at startingto supply excess wattage for a short time after which.l the connectionsare changed to supply normal wattage.

Such controls, however, not only required extra connections but alsoinstrumentalities of a precision nature to operate the connections,which appreciably increased the cost. Moreover, the instrumentalitieswere not directly responsive to the temperature of the heating elementsand by reason thereof were not suiiiciently exact or certain to assureadequate preheating or interruption of the preheating before detrimentalexposure of the heating elements to the high starting heat.

Furthermore, it has been customary to accomplish the preheating byimpressing on the heating elements a higher voltage than that at whichthey are normally intended to operate and this high voltage is likely toshorten the life of the unit and may permanently impair the heatingelement if unduly prolonged. y

The principal objects of the present invention are to provide improvedpreheating facilities in which the preheating is accurately controlledby the temperature in the heating unit at the place where the heat isgenerated for heating the unit; to accomplish the preheating withoutsubjecting the heating resistances to a higher voltage than that atwhich they are normally intended to operate; to avoid extra connectionsand changes of connections for controlling therpreheating; and ingeneral to provide simple and reliable Vfacilities which insure rapidpreheating and avoid the above mentioneddisadvantages of previouspreheating facilities, these and other objects being accomplished aspointed out more particularly hereinafterA and as shown in theaccompanying drawing, which shows a preferred embodiment of theinvention, and in which: Fig. 1 is atop view of a range surface heatingunit 2,763,391 Patented Oct. 2, 1956 made in accordance with the presentinvention and with parts broken away to show details of the constructionand including a somewhat diagrammatic illustration of a control forselective regulation of the operating temperature of the unit;

Fig. 2 is an enlarged cross sectional view of the unit of Fig. 1 takenon the line 2-2 thereof;

Fig. 3 is an enlarged sectional view of the inner closed end of the unitof Fig. l taken on the line 3-3 thereof; and

Fig. 4 is a sectional view on the line 4-4 of Fig. 3 showing theconnection of the resistances to a return conductor at the closed innerend of the heating unit.

In accordance with this invention, the heating unit is composed of atubular metal sheath having a conventional or standard heating elementextending lengthwise in the sheath and embedded in highly compacted heatconductive electrical insulating material by which the heating elementsare electrically insulated from one another and from the sheath, and forpreheating purposes, a special heating element which not only serves tosupply the additional heat for preheating but also controls the extentand duration of preheating, extends lengthwise in the sheath alongsidethe conventional or standard heating element thereof and is electricallyinsulated throughout its length from the conventional heating elementand the sheath, and this special heating element is connected inparallel with the conventional heating element so that the currentsupplied to the heating unit passes parallelly through both of theheating elements and are both simultaneously energized.

Only one conventional or standard heating element and one such specialheating element are shown in the illustrated embodiment of the drawing,but it is to be understood that more than one conventional heatingelement and more than one special heating element may be employed ifdesired.

The heating unit shown in the drawing is similar to and may be made in amanner similar to the heating unit shown and described in Patent2,643,317 to William R. Tuttle, and comprises a tubular metal sheath 10containing two long heating elements 11 and 12 which extend lengthwisein the sheath 10 in side by side spaced apart relation and are embeddedin and electrically insulated from one another and from the sheath by acompacted mass of heat conductive electrical insulating material 13.These heating elements may be of any desired type but preferably are andare shown in the conventional form of helices of resistance wirecomposed of a connected series of spaced apart coils or convolutions asare well known in the art.

In the illustrated embodiment, the sheath 10 and its contents are in aat spiral form, such as employed for range surface units, with a wideattened pan or utensil supporting top face 14, and the particular unithas the sheath closed at the inner end, as indicated at 15, and theother end open with terminals projecting therefrom through which currentis supplied to the heating elements or resistances 11 and 12.

In this heating unit, which is somewhat triangular in shape, theresistances 11 and 12 are located side by side near the top of the unitdirectly under the flat top 14 and a common conductor 16 of lowresistance extends lengthwise of the unit near the bottom thereof in theinsulation 13 and at the closed inner end 12 of the unit is connected tothe inner ends of both resistances 11 and 12, as indicated in Figs. 3and 4, as for example, by the bent wire conductor member 17 which ispermanently secured centrally to the end of the conductor 16 and has thetwo ends thereof inserted and secured in the respective inner ends ofthe resistances 11 and 12.

A terminal 18 leads from the otherend of the con.

duct 16 out through the open end of the sheath 10 and preferably.eachheating element or resistance 11 and 12 has, at its end remote fromthe connector 17, a separate terminal, indicated respectively at 19 band20, which leadsY` Preferably the heating elements 11 and 12 areiof the.ysame voltage rating and for ,operation of the unit current is suppliedsimultaneously to bothheating elements, either from a two wire powersupply, by connecting ther two terminals 19 and 20 to one conductor ofthe two wire feed and the terminal 1S to the other-conductor of the twowire feed, or from a three wirepower supply having a neutral wire inwhich event the neutral wire is connected to theterminal 18 and theother-two power supply wires are connected respectively tothe terminals19 and 20 so that `the same voltage is impressed on each of the heatingelements 11 and'12.

Itis possible, however, to employ heating elements 11 and 12of'different voltage ratings, for example, one for 110-120 voltage andthe other for 220-240 voltage, in which event the neutral of the threewire feed would be connected to the terminal 19 or 20 of the low voltageheating element and the other two feed wires respectively to the otherof said terminals 19 or 20 and the terminal Theheatingelement 11 is ofconventional type, the re-N sistance of which is not appreciably aiectedbychanges of temperature. The heating element 12, however, is made of analloy which has a high temperature coefficient of resistance so that theresistance thereof increases with the temperature and by reason thereofthe wattage cag;

heating element 12 immediately supplies excess heat toyy the unit forpreheating and as the heat thus supplied is dissipated it continues tosupply excess heat, the amount` of which diminishes, however, as theunit is heated until the operatingtemperature of the unit is reached,whereupon the wattage supply to the heating elementv 12 levels off atthe low amount determined by the high resistanceof the heating element12 at the temperature at which the unit operates and the low kwattagesupply is continued so long as that operating temperature ismaintained-- Theheating element 12 may be made, for example,

of anfalloy of -nickel and iron containing about 70% nickel'n and about30% iron, which will .provide a resistance which has atV normal highoperating temperature/of the unit about one fourth the wattage capacityof -the resistance at normal or room` temperature, this being'adesirable range of resistance varlatlon as 1t affords suffi-- cientextra heat for starting and at thesame ,time permits a heating element11 of high wattage-to Vbe employed.-

It is to be noted particularly'that in view ofthe parallell Y connectionof the elements 11 and 12 the heating element 11 operates` duringthe'preheating, but at its normal wattage capacity, and that the heatingelement 12 continues to operate after the preheating period, Vbut at the1 reduced wattage thereof and that in normaloperation of the heatingunit it is heated in part by the element -11 and in part by theelementv12, the initial temporary high wattage of the latter serving asa booster to contributev the necessary additionalvheat for preheatingonly in the starting operations of the unit. l

Preferably, the heating element'` 11 is of such wattage 'Y capacity tosupply the larger proportion of the heat rre-j quired by theheatingrunit in normal operation thereof f and the heating element 12 isofsuch wattagecapacity l' that after its preheating purposeisaccomplished, -it-sup 1 plies only a small amount of the heat requiredby the heating unit thereafter.

For example, in a heating unit of 1250 normal wattage capacity, it ispreferred to employ a heating element 11 having a rated operatingcapacity of 1000 watts and a heating element 12 having a rated operatingcapacity of 1000 watts at normal or room temperature and whichdiminishes to 250 watts at the normal high operating temperature of theunit so that'the major portion of the heating load is imposed on theheating unit 11 in normal operation of the unit. t

Thus the inherent temperatureof the heating element.`

12 is relatively low in vnormal operation and its actual temperature atthat time depends largely upon the heat contributed thereto from theheating element 11V. More-v over, this relative wattagecapacity of theLheating element 11 and parallel connection thereof is advantageous asthe operation of the main heating element 11 is not affected by theauxiliary heating element 12, and accordingly the heating element 11will continue to operate `and to heat the unit to a usable cookingtemperature irrespective of impairment or failure of the heating element12.

The above described heating unit may be employed for full heat only bymerely providing conventional switch controlled or plug-in facilities tomake and break the above described connections to the power supply feedwires, or it may be employed, for example, for high-low 'heating byswitch or plug facilities whi-ch energize the elements 11 and 12conjointly for high heat and the element 12 alone for low heat.

l prefer, however, to employ an infinite control of the type shown inPatent 2,294,573 to Paul H. Potter and Patent 2,503,082 to William R.Tuttle, yand as shown somewhat diagrammatically in the drawing hereof,wherein a shaft21 which operates at a constant rate of speed has cams 22and 23 thereon which operate contacts 24 and 25 respectively to `andfrom other contacts 26 and 27 respectively which are connectedrespectively to the two lines 28 and 29 of a two wire current supply.

The contacts 24 and 25 are carried on spring arms 30 and 31 respectivelywhich are biased to cause engagement of the contacts 24 and 25 withtheir mating contacts 26 and 27 and are moved away from their matingcontacts 26 and 27 by the cams 22 and 23 against the tension of thespring arms 30 and 31 and the spring arm 30 is connected by theconductor 32 with the terminals 19 and 20 of the heating unit so thatthe corresponding ends of the 1 heating elements 11 and 12 are connectedto the line wire 28 when the contacts 24 and 26 are engaged while thespring arm 31 is connected by the conductor 33 to the heating unitterminal `18 so that the other connected ends of the heating yelements11 and 12 (which are at the` closed end 15 ofthe sheath 10) areconnected with the other line wire 29 when the contacts 25 and 27 areengaged.

Thecams 22 and 23 are alike and correspondingly positioned on the shaft21 so. that they impart simultaneous corresponding movement to therespective spring arms 30 and 31.

The contacts 26 and 27 are likewise carried by spring- 'arms 34 and 35respectively which are biased to move said contacts away from theirmating contacts 24 and 25 andV the spring Iarms 34 and 35 engage againstcorresponding cams 36 and 37 on a shaft 38 which is operable by a knob39 to move the cams 36 and 37 in unison and correspondingly so as toadjust the contacts 26 andt27 correspondingly to and from thecontacts 24and 25. y

Thus, by the adjustment of the knob 39, the contacts 26 and 27 can beadjusted out of range of the contacts 24 and 25 to completely interruptthe connection of both -line conductors 28 and29 with the heating unitor they can be adjusted Vso that-the contacts 24 and 25 are notseparable from the contacts 426 and 27 and the connectionsoff the lineconductors with the heating unit are constantly maintained, or saidcontacts 26 'and 27 can be adjusted by "the knob39to anyrintermediateposition between such I constant engagement and constant disengagementof the contacts 26 and 27 with the contacts 24 and 25 so as to provideany desired length of time of engagement of the contacts 24 and 25 withthe contacts 26 and 27 in each rotation of the shaft 21 and the cams 22and 23 thereon.

Thus current may be supplied to the heating unit in. each rotation ofthe shaft 21 for any selected length of time or throughout completerotation of the shaft 21 and thereby heat the unit to 'any desiredintensity and at each occasion of intermittent engagement of thecontacts 24 and 25 with lche contacts 26 and 27 and also on eachoccasion of full time engagement of said contact, both of the elements11 and 12 are energized and accordingly the element 12 is effective uponstarting to use the unit either Iat full heat or at any intermediateintensity of heat to heat the unit quickly to the particular intensityof heat for which the knob 39 is set.

While I have shown and described my invention in its application to aheating unit of range surface type and wherein the current supplyterminals are all located at one end of the heating unit sheath, theinvention is applicable to other types of heating units and other typesof surface heating units and there are various other changes andmodification may be made without departing from the principles of theinvention, the scope of which is to be determined by the appendedclaims.

What is claimed is:

1. An electric range surface heating unit of a predetermined normal highwattage capacity for sustained heating and having excessive temporarywattage capacity substantially in excess of said normal wattage capacityfor quick preheating of the unit, the said unit having an active portioncomprising -a metal tube which is bent in the form of a at winding atone side of which the tube has a wide flat face providing 'at said sidea substantially uniplanar surface on which a utensil is supportable forcon ductivity of heat thereto directly from the aforesaid Wide flat faceof the said metal tube, the said tube having therein a pair ofcorresponding, parallel connected, concurrently energizable helicalresistances which extend lengthwise ofthe tube in laterally spaced apartside-byside relation and are embedded in compacted heat conductiveelectrical insulating material by which the resistances are separatedand electrically insulated from one another and from the tube, one ofthe said resistances having such temperature coeilicient of resistancethat the resistance thereof is substantially constant throughout therange of temperature to which it is subjected in the heating operationof the heating unit, and the other of said resistances having a highpositive temperature coeicient of resistance providing a wide variationof increasing resistance from the low limit to the high limit of therange of temperature to which it is subjected in the operation of theheating unit and affording a wattage capacity at said low limit oftemperature thereof greatly in excess of the wattage capacity at saidhigh limit of temperature thereof, the resistances of said pair beinglocated substantially closer to that side of the winding at which thetube has the wide flat face as aforesaid than they are to the oppositeside of the winding and each said resistance being substantially thesame distance as the other from said wide flat face and substantiallyuniformly distant throughout its length from said at face.

2. A heating unit according to claim 1 wherein the helical resistancesof the pair are correspondingly attened in cross section in a directionperpendicular to the Wide flat face of the tube and are correspondinglyelongated in cross section in a direction paralleling said wide at face.

3. A heating unit according to claim 1 wherein the resistances of thepair are connected in parallel to and simultaneously suppliable withcurrent through la switch which is power operated to interrupt thecurrent supply concurrently to said resistances at optional variableintervals.

References Cited in the le of this patent UNITED STATES PATENTS1,276,589 Steinmetz Aug. 20, 1918 1,393,325 Smith Oct. 11, 19211,510,125 Woodford Sept. 30, 1924 1,767,249 Leckie et al June 24, 19302,110,727 Heinisch et al Mar. 8, 1938 2,400,672 Wiegand May 21, 19462,508,552 Tuttle May 23, 1950 2,575,113 Lennox Nov. 13, 1951

